Ch-3 dig. notes.docx

Chapter3 -- Force and Pressure **EXAMPLES OF PRESSURE IN OUR DAILY LIFE** A. **[Decrease in area increase the pressure]** 1. A nail or a board pin has one end pointed and sharp while the other end is blunt and flat. - This is because, on applying force, the pointed end will exert gre...

Chapter3 -- Force and Pressure **EXAMPLES OF PRESSURE IN OUR DAILY LIFE** A. **[Decrease in area increase the pressure]** 1. A nail or a board pin has one end pointed and sharp while the other end is blunt and flat. - This is because, on applying force, the pointed end will exert greater pressure as the area of contact is small and hence, it will go deep into the given surface. 2. The cutting tools like a blade, knife, axe etc, have very sharp edges. - This is because, the sharp edges have very small area of contact, so the pressure applied by a force is more. 3. A lady with pointed heel sandals finds it difficult to walk on a muddy road than in a tarred road. - This is because, the pointed heels pf footwear exert more pressure on the ground than the regular flat heels. 4. The narrow heeled sandal of a girl hurts more that the broad heeled shoe of a boy. - This is because, more pressure is exerted by the girl than that exerted by the boy as her heel is more narrow than the heel of the shoe of the boy. B. **[Increase in area decreases the pressure]** 1\. Heavy trucks have six to eight tyres instead of the conventional four tyres. - More number of tyres are used to increase the area of contract and thereby reduce the pressure on the ground. 1. A camel can move more conveniently on sand as compared to a horse. - The reason is that the camel has broader feet than that of a horse. - The broader feet of the camel provide lesser pressure on the sand and it becomes easier for the camel to walk. - In the case of a horse, the area of the feet is less, due to which the pressure is more and hence, the feet show a tendency to sink inside the sand, making it difficult to walk. 2. Skiers use long flat skis to slide over the snow. - The larger the area of contact, the lesser is the pressure on the snow. This helps the skier to slide comfortably without sinking in the snow. 3. Army tanks are usually very heavy and they exert large pressure on the ground, id they move on wheels. Hence, they are made to move over the broad steel tracks called **caterpillar wheels of tanks**. - These tracks are used to increase the surface area so as to reduce the pressure on the ground and hence, avoid sinking of their wheels in the ground. 4. Foundation of buildings are kept wide so that the weight of the building may act on larger area. - As a result, it will exert less pressure on the ground. This avoids the sinking of buildings into the earth. 5. A porter wears turban on his head when he has to carry heavy loads. - This helps him in increasing the area of contact of load and head so as to reduce the pressure of load on his head. 6. School bags and shopping bags have broad straps or belts. - So that the area of pressure increases and thus, the pressure on the hand or shoulder is reduced. 7. Wide wooden sleepers are placed below the railway tracks. - So that the pressure exerted by the rails on the ground become less.